A study of techniques to measure and environmental variables influencing the water relations of mesquite (Prosopis glandulosa var. glandulosa torr.)

Abstract

The study of water relations of weedy plants native to arid and semiarid areas, such as mesquite (Prosopis spp.) has received increasing attention in recent years because water is a limiting factor in the development of these areas. The objectives of this study were (1) to investigate the adaption of measurement techniques for estimating water relations of plants to mesquite in situ, and (2) to use controlled environment chambers to evaluate the influence of various soil temperatures, soil moisture levels, and vapor pressure deficits on the amount of water used by mesquite. The studies of measurement techniques to estimate the water relations of mesquite in situ met with varying degrees of success. In studies of the thermoelectric method, a high degree of correlation (r = 0.96) was obtained between water used and the product of the cross-sectional area of the stem and the relative sap velocity for trees less than 1 centimeter in diameter. The correlation decreased as the size of the trees increased due to increasing variability in the conducting tissue (xylem). The results of a study of the beta ray gauging technique using Bi-210 and Tl-204 as sources of radiation for estimating the moisture content of mesquite leaflets were negative. Mesquite leaflets are very small and there was a difference of only 300-400 counts per minute between turgid and dry leaves. Because of the variable structure of mesquite stems, negative results also were obtained from a study of the relationship between diffusivity and the moisture content of the stems of mesquite. A study of the relationship between a linear measurement of the doubly pinnate leaves of mesquite and leaf area produced the equation Log Y = -0.456 + 1.697X [line break] r = 0.96 where Y was the total leaf surface area and X was the sum of the rachis lengths. ...